1. FIELD OF THE INVENTION
The present invention relates to an intermediate accessory, such as a rear converter, an extension tube and a bellows, which is mounted or interposed between a camera body and an interchangeable lens, and relates to a camera system in which said intermediate accessory is interposed. More particularly, the invention relates to such an accessory for use in a photographic camera system wherein various constant and variable data inherent to the objective lens, such as the maximum and minimum F-numbers, the focal length, data indicative of the relationship between the direction of the rotation of a motor in an automatic focus camera body and the direction of the movement of the lens system, and data indicative of the relationship between the amount of the rotation of said motor and the amount of the shifting of the in-focus position, are transmitted from the interchangeable lens to the camera body, the data are processed and the resultant data are used for automatic exposure control, automatic focus control, and various warnings and indications.
2. DESCRIPTION OF THE PRIOR ART
Generally, an intermediate accessory is interposed between the camera body and the interchangeable lens, thereby enabling a close photograph or extending the focal length of the photographic optical system. Moreover, with the progress of camera technology in recent years, the converter is provided so as to operate the automatic exposure control device and automatic focusing device. However, when more than one converter is interposed between the camera body and the interchangeable lens opposition to the maker's design, there occurs a lowering of the performance of the automatic exposure control device, a lowering of the precision of the automatic focusing device, furthermore a problem of the strength of the driving speed reduction system in the automatic focusing device.
To describe in detail, in FIGS. 1 and 2, a rear converter lens 3 comprises a rear converter lens system L.sub.C. Bayonet mounting member 31 in the rear side (in the right side in FIGS. 1 and 2) and bayonet mounting plate 32 in the front side (in the left side in FIGS. 1 and 2) form interconnecting means for interconnecting the rear converter lens 3 respectively to the camera body 1 and to the interchangeable lens 2. Reference numerals 33 and 34 respectively denote a mediating submission shaft and a mediating driving output shaft, which are disposed coaxially with each other a connection concave portion 33a is formed on the rear end portion of the mediating submission shaft 33, to be engaged with a driving output shaft 30 of the camera body 1 a connection convex portion 34a is formed on the front end portion of the mediating driving output shaft 34, to be engaged with a submission shaft 50 of the interchangeable lens 2. The mediating submission shaft 33 is supported between the bayonet mounting member 31 and a shaft supporting plate 35. On the front end portion of the mediating submission shaft 33 passing through the shaft supporting plate 35, there is fixedly provided a gear 39 to be engaged with a gear 38 which is fixedly provided around the one side portion of a relay shaft 37 which is supported between the shaft supporting plates 35 and 36. The mediating driving output shaft 34 is supported between the bayonet mounting plate 32 and the shaft supporting plate 36. On the rear end portion of the mediating driving output shaft 34 there is fixedly provided a gear 41 engaging with another gear 40 fixed to the relay shaft 37. The mediating driving output shaft 34 comprises a flange portion 34b, and a spring member 42 is interposed between the flange portion 34b and the shaft supporting plate 36, so that the convex portion 34a is forced to be projected from the bayonet mounting plate 32 by the spring member 42. However, when a connection release button 43 is depressed, a connection plate 44 connected to the connection release button 43 through a mechanism (not shown) pushes the flange portion 34b backward, so that the mediating driving output shaft 34 is moved to the position against the spring 42 so as to sink the convex portion 34a into the bayonet mounting plate 32. The gears 38, 39, 40 and 41 together with the relay shaft 37 compose a drive transmission system transmitting the rotation of the mediating submission shaft 33 to the mediating driving output shaft 34, which is designed as a speed reduction system when the rear converter lens system L.sub.C works as a tele-converter.
In FIG. 2 showing a condition that the rear converter lens 3 is mounted between the camera body 1 and the interchangeable lens 2, the driving output shaft 30 is projected from the mounting plate 30a in the camera body 1. Reference numeral 45 denotes a movable main mirror in a single lens reflex camera, and a light passing through a transparent portion formed in the center portion of the movable main mirror 45 is reflected by a subsidiary mirror 46 so as to be applied to a focus detecting element 47. Herein, the light receiving surface of the focus detecting element 47 is disposed on the position optically equivalent to the film surface, i.e., the predetermined focal plane in the camera body 1. Reference numeral 48 denotes a control circuit generating a signal representing the defocus direction and a signal representing the defocus amount on the basis of the output of the focus detecting element 47, thereby controlling the driving direction and the driving amount of a driving motor M in the camera body 1. The motor M drives a gear 30b fixed to the driving output shaft 30 through a suitable gears line composing a driving transmission system.
On the other hand, the interchangeable lens 2 comprises bayonet mounting member 52 in the rear end portion thereof and comprises an optical system L.sub.E working as a focusing optical system inside thereof. Although the interchangeable lens 2 shown in FIG. 2 is a type of moving the entire part of the optical system L.sub.E and the entire optical system forms a focusing optical system, a part of the optical system may be used as a focusing optical system. The rotation of the submission shaft 50 is transmitted through a gears line composing a drive transmitting system to a helicoid screw member 54 which is a focusing optical system moving mechanism so as to rotate the helicoid screw member 54, whereby helicoid screws 56 and 59 are operated so as to move the focusing optical system L.sub.E in the direction of the optical axis thereof.
By the way, if the interchangeable lens 2 is directly mounted on the camera body 1 without interposing the rear converter lens 3, the data signals inherent to the interchangeable lens 2 are applied to the control circuit 48 in the camera body 1. That is, in the interchangeable lens 2 there is provided ROM (read only memory) 58 storing a value K.sub.M inherent to the interchangeable lens 2, wherein the value K.sub.M represents the ratio of the rotation of the submission shaft 50 to the defocus amount thereby as follows. EQU K.sub.M =k.sub.M /l.sub.M..mu..sub.M ( 1)
Herein, k.sub.M : the ratio (=.DELTA.d/.DELTA.L) of the amount .DELTA.L of moving the focusing optical system L.sub.E to the defocus amount .DELTA.d
.mu..sub.M the gear ratio of the drive transmitting system (.mu..sub.M &lt;1 at the time of speed reduction system)
l.sub.M : the lead of the helicoid screw 56
On the contrary, as shown in FIG. 2, if that the rear converter lens 3 is interposed between the interchangeable lens 2 of a type of moving the entire optical system for focusing operation and the camera body 1, the ratio K.sub.M of the amount of moving the focusing optical system L.sub.E to the defocus amount is changed due to the conjunction of the focusing optical system L.sub.E and the rear converter lens system L.sub.C. Assuming that the ratio of the amount of moving the focusing optical system L.sub.E to the defocus amount when the rear converter lens 3 is interposed, which is inherent to the conjunct entire optical system, is K.sub.MC, the ratio K.sub.MC is shown as follows, EQU K.sub.MC =(f.sub.M /f.sub.MC).sup.2 ( 2)
wherein f.sub.M : the focal length of the focusing optical system L.sub.E only of the interchangeable lens,
f.sub.MC : the compound focal length of the conjunction system of the focusing optical system L.sub.E and the rear converter lens system L.sub.C. Herein, assuming that the magnification (referred to as MAGNIFICATION hereinafter) of the rear converter lens system L.sub.C is M, since f.sub.MC =M.f.sub.M, results in K.sub.MC =M.sup.-2.
Accordingly, in this case the ratio K.sub.MC of the rotational frequency of the submission shaft to the defocus amount in the conjunction optical system is represented as follows, ##EQU1## wherein
.mu..sub.C : the gear ratio of the drive transmitting system provided in the rear converter lens 3,
.eta..sub.C : the transmission coefficient of the signal transmitting system.
In other words, the product of the multiplication of the transmission coefficient .mu..sub.C of the drive transmitting system in the rear converter lens 3 and the transmission coefficient .eta..sub.C of the signal transmitting system is determined by the MAGNIFICATION of the rear converter lens 3. For example, in case of the tele-converter lens of which the MAGNIFICATION rate is two, the production value .eta..sub.C..mu..sub.C should be 1/4, therefore, the values .eta..sub.C and .mu..sub.C are set as follows, for example, EQU .eta..sub.C =1/2, .mu..sub.C =1/2 or .eta..sub.C =3/4, .mu..sub.C =1/3.
Herein, in the case of the tele-converter in which the focal length of the conjunct optical system is longer than that of only the interchangeable lens, since the ratio of the moving amount of the focusing optical system to the defocus amount becomes small from the expression (2), the minimum amount of the displacement of the image plane becomes large and the speed of the movement of the focusing optical system to the in-focus condition becomes large so that the focusing optical system does not stop in the in-focus condition so as to exceed the in-focus position, which results in the deterioration of the precision of the focusing optical system. Therefore, upon setting the gear ratio .mu..sub.C of the drive transmitting system to the speed reduction system, the driving speed of the drive transmitting system is reduced so as to raise the focusing precision of the focusing optical system. However, the driving torque becomes large and the load applied to the stopper located at the infinity focusing position of the focusing optical system and at the closest focusing position thereof becomes large. Furthermore if two or more converter lenses are interposed by mistake between the interchangeable lens 2 and the camera body 1, further larger load is applied to the stoppers by the speed reduction driving system of the interchangeable lens 2 and the converter lenses, thereby causing possible damage to the stoppers.
In order to solve the inconveniences mentioned above, there may be considered a mechanism in which two or more converter lenses can not be interposed because of the mechanical interference of the mounting portion, but in this case there is a defect that the mounting portion becomes complicated. Though the transmission of data signals through a single converter lens has been disclosed in U.S. Pat. No. 4,572,638, is not disclosed that data signals transmitted through a plurality of converter lens interposed in the camera system are used to inhibit a camera operation.